Flame retardant adhesives and tapes are used in many industries and for many different purposes. They are used, for example, in the electrical industry as insulating tapes. Many conventional flame retardant compositions, widely used as flame retardant adhesives and tapes, utilize one or more halogen-containing materials.
Pressure sensitive adhesive (PSA) tapes are used in a variety of applications with elevated fire/flame risk (aircrafts, cars, trains, ships, electrical wiring, electronics, etc.). Polymer-based PSAs can be flammable and a variety of flame retardants are used to minimize the fire/flame risk associated with the use of PSAs for specific applications. Flame retardants can reduce the flammability of materials by a variety of mechanisms including: quenching free radicals in the gas phase; reacting with chemical fragments from the burning material to initiate char formation; and forming barrier layers within the burning material.
Commonly used flame retardants include halogenated compounds (e.g. polychlorinated biphenyl and polybrominated diphenyl ethers). These flame retardants are well-known and very efficient at fire retardation in combustible materials. However, many compounds in this class of flame retardants are considered hazardous substances. Several of the most effective halogenated flame retardants have been banned by the European Union under the Restriction of Hazardous Substances (RoHS) since Jul. 1, 2006. Several Asian countries and individual states in the United States are also following with similar RoHS directives. In addition, end-product manufacturers are establishing policies to refuse to use halogenated flame retardant materials in their products.
Thus, environmental and safety concerns regarding use of halogen-containing materials in adhesives and related articles have been raised and in response to these concerns, many non-halogenated or halogen-free flame retardant materials have been introduced to be used in place of halogen-containing materials. Phosphorus-based compounds are one class of non-halogenated flame retardants which have been applied to replace halogenated flame retardants in many applications.
A current method to flame retard adhesives and additional polymeric materials is to blend halogenated or phosphorus containing flame retardant additives into the product formulation. However, a disadvantage of this approach is the flame retardant additive can leach out of the product over time. This reduces the flame retardancy of the product. It can also cause potential health and safety concerns related to exposure to harmful flame retardants that have leached out of blankets, clothing, and other commonly used items. In addition, flame retardant materials that migrate to the surface of an adhesive composition can reduce its adhesion strength. Furthermore, care must be taken in the preparation of these adhesive blends to thoroughly mix the flame retardant additive into the adhesive. If the flame retardant is poorly distributed or not miscible throughout the adhesive, regions of the adhesive having a relatively low amount of flame retardant can be less flame retardant than regions of the adhesive having a relatively higher amount of flame retardant.